Concrete Construction

Design of RCC Slab Roof

Design RCC Slab

Formwork for Concrete Construction, ShutteringDesign of RCC Slab Concrete Slab Reinforced Concrete Slab is one of the most important components in Residential building. Concrete Slab Structural elements of modern buildings. Flab slab construction for Roof Slab supported on Columns and beams. Reinforced Cement Concrete slabs are thickness ranges from 4inch to 6inches are most often used for the construction of floors and ceilings.

Design of RCC Slab ROOF, Calculations, Precautions

Concrete Slabs are also used for the Exterior paving Purpose. Design of Simply Supported Slabs and Design of RCC Structures details discussed here. Simply supported slabs are supported on columns. The slab has support on all four sides. as we discussed earlier, Slabs are classified into two types One-way slab and two-way slabs. One way slabs bend in one direction only and transfer their loads to two end support beams in opposite directions. On oneway slabs main steel in on shorter span length, For one way slab, L/B ratio is generally less than 2.

Two-way slabs bend in both directions, transfer their loads and stresses on all four sides. L/B Ratio is equal to or greater than 2. A concrete roof or slab is made waterproof by applying stabilized bitumen sheets. RCC Roof designs, movements. The floor is first cleaned and then some bitumen is sprinkled over the surface and then bitumen stabilized sheets are rolled over the surface and joined with other at edges by applying heat through the gas torch. RCC Slab roof dimensions by footing sizes. RCC Slab Design depends on the dimensions of the slab after which the slab is termed as a one-way slab or a two-way slab

Check Out: Differences Between One Way Slab vs Two Way Slab

Reinforced Concrete Slab Designs

  • Effective Span of Slab
  • Depth of Slab
  • Load on a slab [ Dead loads, live loads ]
  • Detailing requirements of Reinforcement cover Nominal cover
  • Minimum reinforcement
  • Spacing of Bars
  • Maximum diameter of Bar

1) Effective Span of Slab

Calculating Distance between center to center of support and Clearspan plus effective depth

L/B = 2
L = clear span + d (effective depth)
L = Center to center spacing among the support

Minimum main reinforcement
0.15% gross c/s of the slab – for MS bars
0.12% gross c/s of the slab – for HYSD bars

Reinforcement design

A one-way slab has structural strength in the shortest direction.
A two-way slab has structural strength in two directions.

Depth of Slab

Depth of slab: The depth of the slab is influenced by the bending moment and deflection criterion. The trail depth is achieved with the following:-

Effective depth d = Span/((L/d) Basic x modification factor)
The effective depth d of two slabs is also taken as cl.24.1, IS 456 on the condition that short span is 3.5m and loading class is <3.5KN/m2.

Nominal Cover:

For Mild Exposure: 20mm
For Moderate Exposure: 30mm

The Diameter of the bar does not exceed 12mm, or cover may be reduced by 5mm. Main reinforcement up to 12mm diameter bar and for mild exposure. Nominal Cover 15mm. The diameter of Bars varies from 8mm to 14mm and should not exceed 1/8th. Overall depth of the slab.


For reinforced concrete slabs, reinforcing steel bars are placed within the formwork and then the concrete is poured. Plastic tipped metal, or plastic bar chairs are used to hold the reinforcing steel bars away from the bottom and sides of the form-work, so that when the concrete sets it completely envelops the reinforcement. Formwork differs with the kind of slab. For a ground slab, the form-work may consist only of sidewalls pushed into the ground whereas for a suspended slab, the form-work is shaped like a tray, often supported by a temporary scaffold until the concrete sets.

formwork construction and setting up is commonly built from wooden planks and boards, plastic, or steel. Formwork is all about setting for construction movement. On commercial building sites today, plastic and steel are more common as they save labor. The slab is square and the restraint is similar along the four sides, then the load will span equally in both directions.

For distribution steel, the diameter varies from 6mm to 8mm. The bottom cover for reinforcement shall not be less than 15mm or less than the diameter of such a bar. Normally columns casting is left down up to 50D of f=dia of beam reinforcement. Then the beam is placed with its legs inserted in columns. Then beam and columns caps are cast monolithically. The distance of the bar, The maximum distance of bars should not surpass.

RCC Slab Precautions

Cracks are the most faced issue. Residential or commercial suffer from cracks and leakages in their slabs. Heavy repair and Maintenance is major thing to carry design life. These cracks provide a point of entry for the water and the aggressive chemicals dissolved in this water to enter the slab. Mainly cracks is caused due to improper design of concrete mix with perfect proportion, Improper placing practices of concrete. Reasons due to cracks, shrinkage of fresh concrete. Cracking due to intrinsic sulfate attack, cyclic loading, and alternate wetting. For construction the slab, Selectin of right materials and uses plays an important role in durability by concrete.


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